Hybrid Spectral Domain Optical Coherence Tomography Line Scanning Laser Ophthalmoscope

ABSTRACT

A method of imaging a retina of an eye includes combining an optical path of an optical coherence tomography (OCT) imager and an optical path of a line scanning laser ophthalmoscope (LSLO) imager using a system of optics. The method also includes using a single detector to switch between an OCT mode and a LSLO mode and acquiring images of the retina while switching between the OCT mode and the LSLO mode.

This application is a divisional of prior co-pending application Ser.No. 12/964,518, filed on Dec. 9, 2010, which is a divisional ofapplication Ser. No. 12/630,358 filed on Dec. 3, 2009, now U.S. Pat. No.7,866,821, which is a divisional of application Ser. No. 11/799,315filed on May 1, 2007, now U.S. Pat. No. 7,648,242, which claims thebenefit of and priority to U.S. Provisional Patent Application No.60/796,387 filed May 1, 2006, all of which are owned by the assignee ofthe instant application and the disclosures of which are incorporatedherein by reference in their entireties.

STATEMENT OF GOVERNMENT INTEREST

This invention was made with government support under Air Force ContractNo. FA9550-05-C-0181. The government may have certain rights in theinvention.

FIELD OF THE INVENTION

This invention relates generally to optical imaging, and moreparticularly, to a device that combines a line-scanning laserophthalmoscope and a spectral domain optical coherence tomography systemfor retinal imaging.

BACKGROUND OF THE INVENTION

Fundus and retinal imaging are important diagnostics in ophthalmology.Advanced imaging technologies now exist to detect tissue changes thatoccur due to retinal injuries not discernable with fundus photography.For example, optical coherence tomography (OCT) can providedepth-resolved images of ocular tissues approaching cellular resolution.The confocal scanning laser ophthalmoscope (SLO) also plays an importantrole in high-contrast visualization of thermal and other damage nearsensitive retinal anatomy (e.g., the fovea).

OCT is an emerging technology for micrometer-scale, cross-sectionalimaging of biological tissue and materials. A major application of OCTis ophthalmic imaging of the human retina in vivo. The Spectral-DomainOCT (SDOCT) improvement of the traditional time domain OCT (TDOCT)technique, known also as Fourier domain OCT (FDOCT), makes thistechnology suitable for real-time cross-sectional retinal imaging atvideo rate. At high speed, the need for vertical realignment of “A-scan”depth profiles is effectively eliminated across single B-scans,revealing a truer representation of retinal topography and the opticnerve head. Although B-scan image distortion by involuntary eye movementis reduced, transverse eye motion remains an issue for 3-D imaging andindividual scan registration. Stabilized 3D OCT imaging can provide anen face fundus views for locating any given B-scan relative to retinallandmarks. Alternatively, simultaneous or interleaved live fundusimaging can also provide good retinal coordinates for a given B-scan,subject to the limitations of inter-frame eye motion.

The fusion of wide-field, line scanning laser ophthalmoscope (LSLO)retinal imaging with SDOCT imaging can enhance the clinician's abilityto quickly assess pathologies in linked, complementary views with asimple, compact instrument. To make the ocular interface of future SDOCTsystems more efficient, cost-effective, compact, and eventually fieldportable, neither complex motion stabilization systems noropto-mechanical integration of secondary fundus cameras are desirable.Yet without precise knowledge of the OCT scan coordinates within thelive fundus image to guide scan acquisition and interpretation, thediagnostic utility of this powerful imaging modality is limited.

The model for most clinical imaging systems to date has been the largestationary, desk-sized platforms with slit-lamp style human interface,bulky enclosure, numerous secondary optical or physical adjustmentfeatures, tethered power conditioning and signal processing units,computer, mouse and keyboard, and CRT monitor. These units generallyrequire the subjects to adapt their posture to the instruments, ratherthan vice-versa. They typically combine the user interface and imageacquisition functions with the image processing functions, the imageanalysis functions and the patient database. What is needed is animaging system that can adapt to the patient, one where the operator,technician or medic can gather data, and an eye injury expert canprovide analysis remotely based on the data recorded.

SUMMARY OF THE INVENTION

The invention, in one embodiment, features a system to provide images ofthe retina of an eye using a single compact instrument. The retinalimaging system can be a combination of an OCT system (e.g., a SDOCTsystem) and a LSLO system. In some embodiments, the SDOCT and LSLO sharethe same imaging optics and line scan camera for both OCT and LSLOimaging modes. Co-registered high contrast wide-field en face retinalLSLO and SDOCT images can be obtained non-mydriatically with less than600 microwatts of broadband illumination at 15 frames/sec. TheLSLO/SDOCT hybrid instrument can have important applications in clinicalophthalmic diagnostics and emergency medicine. The fusion of thewide-field, LSLO retinal imaging with SDOCT imaging can enhance theclinician's ability to quickly assess pathologies in linked,complementary views with a simple, compact instrument. Knowledge of theOCT scan coordinates within the live fundus image to guide scanacquisition and interpretation can enhance the diagnostic utility ofOCT. For example, non-mydriatic, live retinal imaging (no pupildilation), which requires no more than a 3 mm pupil in the human eye,usually depends on the use of NIR illumination to inhibit the pupilclosure reflex. This is the case for the broadband SLD illumination beamfrom 800 nm to 900 nm, which for most subjects is still visible at <1mW, but not bright or aversive, and allows imaging through a natural 2to 3 mm pupil under subdued lighting conditions. The integration ofhand-held LSLO technology with SDOCT can use the 3 mm pupil of the eyein two ways. First, the central 1 mm portion of the pupil is used as theSLD beam entrance pupil for both subsystems, but the exit pupils areseparated. The returning light of the SDOCT passes back though the same1 mm pupil, to function as an interferometer. The LSLO system can usethe 3 mm annular aperture surrounding the central pupil area as its exitpupil for imaging the scattered light from the retina, thereby alsoavoiding corneal reflections from the entrance pupil. Second, the leftand right sub-apertures of the LSLO annular aperture can be imaged toleft and right detector arrays in order to form an LSLO stereo pair.This may be useful for direct visual assessment of gross retinalfeatures and damage such as retinal hemorrhage.

In one aspect, there is an apparatus that includes a housing and asystem of optical components disposed in the housing. The opticalcomponents are capable of operating in a LSLO mode and an OCT mode. Theoptical components include a first source to provide a first beam oflight for the OCT mode, a second source to provide a second beam oflight for the LSLO mode, and a first optic. In the OCT mode, the firstoptic scans, using a first surface of the first optic, the first beam oflight along a retina of an eye in a first dimension and descans usingthe first surface, a first light returning from the eye in the firstdimension to a detection system. In the LSLO mode, the first opticpasses the second beam of light to the retina of the eye through asecond surface of the first optic.

In another aspect, there is an apparatus that includes a housing and asystem of optical components disposed in the housing capable ofoperating in an LSLO mode and an OCT mode. The system of opticalcomponents includes a first optic. In the OCT mode, the first opticredirects, using a first surface of the optic, a beam of light from afirst source to an object to be scanned. The first optic also uses thefirst surface to redirect light returning from the object scanned. Asecond surface of the first optic redirects light dispersed by a gratingto a detection system. In the LSLO mode, the first optic passes lightreturning from the object scanned to the detection system.

In another aspect, there is a method for imaging a retina of an eye. Themethod includes acquiring an OCT image of the eye by receiving, on aone-dimensional detector, a first light returning from the eye. A firstelectrical signal responsive to the first light is provided at each of aplurality of locations along the one-dimensional detector. The firstelectrical signal is combined with a reference signal from a referencearm. The first electrical signal and the reference signal is associatedwith the OCT image of the eye. In the LSLO mode, the method includesacquiring a LSLO image of the eye by receiving, on the one-dimensionaldetector, a second light returning from the eye. A second electricalsignal is provided which is responsive to the second light at each of aplurality of locations along the one-dimensional detector. The secondelectrical signal is indicative of the LSLO image of the eye. The methodalso includes interleaving acquisition of the OCT image of the eye andthe LSLO image of the eye.

In yet another aspect, there is an optical apparatus including a linescanning laser ophthalmoscope (LSLO) mode and an optical coherencetomography (OCT) mode. The optical apparatus includes a first source ofa beam of light suitable for use in the LSLO mode and a second source ofa beam of light suitable for use in the OCT mode. A lens receives thebeam of light from the first source and provides a line of light for usein the LSLO mode. The apparatus also includes an optic. In the OCT mode,the optic redirects a beam of light from the second source to an objectto be scanned, using a first surface of the optic. The optic uses thefirst surface to redirect the light returning from the object scannedand uses the second surface of the optic to redirect light dispersedinto an OCT line configuration by a grating to a detection system. Inthe LSLO mode, the optic passes light returning from the object scannedto the detection system. The optic apparatus also includes a scanner. Inthe LSLO mode, the scanner scans a first portion of an object with theline of light in a direction perpendicular to the line through at leastone lens. The scanner also descans light returning from the object in aLSLO line configuration. In the OCT mode, the scanner scans a secondportion of the object with the beam of light and redirects lightreturning from the object. The detection system includes aone-dimensional detector. In the LSLO mode, the detection systemreceives the light descanned from the object and provides an electricalsignal responsive to the light descanned at each of a plurality oflocations along the LSLO line configuration. The electrical signal isindicative of a LSLO image of the object. In the OCT mode, the detectionsystem receives the light redirected from the mirror and provides anelectrical signal responsive to the light redirected at each of aplurality of locations along the OCT line configuration. The detectionsystem combines the electrical signal with a reference signal from areference arm. The electrical signal and the reference signal isassociated with an OCT image of the object.

In another aspect, there is a method of imaging a retina of an eye. Themethod includes combining an optical path of an OCT imager and anoptical path of a LSLO imager using a system of optics. A singledetector is used to switch between an OCT mode and a LSLO mode. Themethod also acquires images of the retina while switching between theOCT mode and the LSLO mode.

In another aspect, there is an optical apparatus that includes a housingand a system of optical components disposed in the housing capable ofoperating in a line scanning laser ophthalmoscope (LSLO) mode and anoptical coherence tomography (OCT) mode. The system of opticalcomponents includes a lens for converting between the LSLO mode and theOCT mode. The lens is movable between a first lens position and a secondlens position. In the first lens position, the lens receives a beam oflight from a source and provides a line of light for scanning an objectin the LSLO mode. In the second lens position, the lens removed from apath of the beam of light so that the source provides the beam of lightfor scanning the object in the OCT mode. The optical apparatus alsoincludes a mirror for converting between the LSLO mode and the OCT mode.The mirror is movable between a first mirror position and a secondmirror position. In the first position, the mirror is removed from apath of light returning from the object. In the second position, themirror receives the light returning from the object.

In other examples, any of the aspects above, or any apparatus or methoddescribed herein, can include one or more of the following features.

In some embodiments, the first optic includes a beam separator having anaperture that, in the LSLO mode, redirects the second light returningfrom the eye to the detection system. In some embodiments, the opticalsystem can include a dichroic beamsplitter. In some embodiments, thefirst optic is a dichroic beam splitter. The dichroic beam splitter canbe disposed in the aperture. In the OCT mode, the dichroic beam splitterdisposed in the aperature uses the first surface of the dichroic beamsplitter to scan the first beam of light along the retina of the eye inthe first dimension and uses the first surface to descan the first lightreturning from the eye in the first dimension to the detection system.In the LSLO mode the second beam of light to the retina of the eyepasses through the second surface of the dichroic beam splitter.

In some embodiments, the system of optical components also includes asecond optic that, in the OCT mode, scans the first beam of light alongthe retina in a second dimension and descans the first light returningfrom the eye in the second dimension. The second optic can direct thefirst light returning from the eye to the first surface of the firstoptic and to the detection system. In the LSLO mode, the second opticcan scan the second beam of light, in a line focus configuration, alongthe retina in the second dimension, and descan the second lightreturning from the eye in the second dimension. The second optic candirect the light returning from the eye to the first surface of thefirst optic and to the detection system. In some embodiments, the secondoptic includes a scanning mirror.

In some embodiments, the system of optical components also includes athird optic. In the OCT mode, the third optic can use a first surface ofthe third optic to direct the first beam of light to the first optic.The third optic can also use the first surface of the first optic toredirect the first light returning from the eye scanned. In someembodiments, the third optic uses a second surface of the third optic toredirect the first light, dispersed by a grating, to the detectionsystem. In the LSLO mode, the third optic can pass the second lightreturning from the eye to the detection system. The third optic caninclude a dichroic beam splitter.

In some embodiments, the housing is adapted to be handheld. The firstsource and the second source can be the same source of light. In someembodiments, the imaging apparatus includes a controller, associatedwith the detection system, that switches the apparatus between the OCTand the LSLO mode. The controller associated with the detection systemcan also interleave the acquisition of the OCT image of the eye and theLSLO image of the eye by the detection system. In some embodiments, theOCT mode includes a spectral domain OCT mode.

In some embodiments, the system of optical components can include ascanner. In the LSLO mode, the scanner can scan through at least onelens, a first portion of the object with the line of light in adirection perpendicular to the line. The scanner can also descan lightreturning from the object in the LSLO line configuration. In the OCTmode, the scanner can scan a second portion of the object with the beamof light and redirect light returning from the object.

In some embodiments, the system of optical components includes a gratingspectrograph, used only in the OCT mode, to disperse light returningfrom the object into an OCT line configuration.

The apparatus can have a first and second source of light that generatesa first and second light beam. The first and second light beam can beused for the LSLO mode and the OCT mode, respectively. In someembodiments, the detection system includes a one-dimensional detector.In the OCT mode, the one dimensional detector can receive the firstlight returning from the eye in the first dimension and provide a firstelectrical signal responsive to the first light at each of a pluralityof locations along the one-dimensional detector. The first electricalsignal can be combined with a reference signal from a reference arm. Insome embodiments, the first electrical signal and the reference signalis associated with an OCT image of the eye. In the LSLO mode, the onedimensional detector can receive a second light returning from the eyeand provide a second electrical signal responsive to the second light ateach of a plurality of locations along the one-dimensional detector. Insome embodiments, the second electrical signal is indicative of a LSLOimage of the eye.

In some embodiments, the system of optical components includes a sourceof the beam of light used in the LSLO mode and the OCT mode. Thedetection system can include a one-dimensional detector. In the LSLOmode, the detector can receive light descanned from the object andprovide an electrical signal responsive to the light descanned at eachof a plurality of locations along a LSLO line configuration. In someembodiments, the electrical signal is indicative of a LSLO image of theobject. In the OCT mode, the detector can receive light redirected bythe mirror and provide an electrical signal responsive to the lightredirected at each of a plurality of locations along an OCT lineconfiguration. The electrical signal can be combined with a referencesignal from a reference arm. In some embodiments, the electrical signaland the reference signal is associated with an OCT image of the object.

In some embodiments, the apparatus includes a controller, associatedwith the detection system, that switches the apparatus between the OCTmode and the LSLO mode. The controller, associated with the detectionsystem, can interleave acquisition of the OCT image of the eye and theLSLO image of the eye by the detection system. In some embodiments, thecontroller can interleave a first series of images of the retinaacquired in the OCT mode and a second series of images of the retinaacquired in the LSLO mode.

Other aspects and advantages of the invention can become apparent fromthe following drawings and description, all of which illustrate theprinciples of the invention, by way of example only.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages of the invention described above, together with furtheradvantages, may be better understood by referring to the followingdescription taken in conjunction with the accompanying drawings. Thedrawings are not necessarily to scale, emphasis instead generally beingplaced upon illustrating the principles of the invention.

FIG. 1 is a schematic drawing of a hybrid OCT/LSLO retinal imagingsystem.

FIG. 2 is another schematic drawing of a hybrid OCT/LSLO retinal imagingsystem.

FIG. 3 is a schematic drawing of the command lines, imaging raster, andtiming sequence of a hybrid OCT/LSLO retinal imaging system.

FIG. 4 is a schematic drawing of an apparatus that uses moving parts toconvert between the OCT mode and the LSLO mode, according to anillustrative embodiment.

FIG. 5 is another schematic drawing of an apparatus that uses movingparts to convert between the OCT mode and the LSLO mode.

FIG. 6 is a block diagram of an exemplary chipset for use in a hybridOCT/LSLO retinal imaging system.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an embodiment of an imaging apparatus 6 that can provideline scanning laser ophthalmoscope (LSLO) images and Optical CoherenceTomography (OCT) image. The imaging apparatus 6 can be converted betweena LSLO mode and a OCT mode without the use of moving parts. Instead, asystem of optical elements are implemented to combine the beam paths ofthe OCT and the LSLO and to scan an eye 34. A first source 10 provides afirst beam of light for the OCT mode and a second source 14 provides asecond beam of light for the LSLO mode. The imaging system 6 can operatein the LSLO and the OCT mode using optical elements 18, 22, and 26.

When the imaging apparatus 6 is operating in the OCT mode, the beam oflight from the OCT light source 10 travels to a first surface of theoptical element 26, which directs the light to a first surface ofoptical element 18. The line can be redirected to optical element 22,which scans the beam of light along the retina of the eye 34. In someembodiments, the light travels through a system of scanning lenses 38,which adjusts the focus of the light from the OCT source 10. The lightreturning from the eye 34 can be descanned by the optical element 22 anddirected to the first surface of the optical element 18. The firstsurface of optical element 26 directs the light to a waveguide thatdelivers the light to a detector arm. The light is dispersed by agrating 46, and the dispersed light is redirected by the second surfaceof the optical element 26 to an imaging lens 50 that focus the light ona detection system 54.

When the imaging apparatus 6 is operating in the LSLO mode, acylindrical lens 58 can be used to fan out the beam of light from theLSLO source 14 into a line on the retina of the eye 34. The line oflight from the cylindrical lens 58 passes through a second surface ofthe optical element 18. Optical element 22 scans the beam of light onthe retina of the eye 34. Lenses 38 can focus the light on the retina ofthe eye 34. The light returning form the eye 34 can be descanned by theoptical element 22 and redirected by the first surface of opticalelement 18. In the LSLO mode, the light passes through the opticalelement 26, and a system of imaging lenses 50 focuses the light on thedetection device 54.

In some embodiments, a single source can be split to form the OCT source10 and the LSLO source 14. The single source can be switched between anLSLO mode and an OCT mode to deliver light as the LSLO source 14 or theOCT source 10, respectively. In some embodiments, the OCT source 10 andthe LSLO source 14 are two distinct sources.

A single broadband source can be split between two input fibers, or withdual super-luminescent diode (SLD) sources 10 and 14, which can bemodulated. A single broadband source can also be switched between twoinput fibers, or with dual SLD sources 10 and 14 which can be modulated.A broadband superluminescent diode can reduce speckle noise in an SLOimage. Wavelength separation can be achieved by modulating thedual-input fiber-coupled sources electronically, either as dual-SLDsources directly, or by separate fiber-optic switching or modulation ofsub-bands of a single source. This approach is still compatible withsingle source operation, but wavelength or polarization separation canbe employed, along with source-switching or modulation.

The OCT source 10 can be a near-infrared source, such as a 830-nm laserdiode, an 830-nm SLD, or an 800-nm SLD with 30-nm bandwidth availablefrom Exalos Inc. The LSLO source 14 can be a substantially point sourceof light, such as an infrared laser or a super-luminescent diode. Forexample the LSLO source 14 can be 905-nm SLD or a 920 nm SLD. In oneembodiment, the OCT source 10 is a broadband super-luminescent diode(SLD-37MP, Superlum-Russia) with 830 nm central wavelength andapproximately 50 nm bandwidth, and the LSLO source 14 is a 920 nm SLD(QSDM-920-2, Q-Photonics) with about 35 nm FWHM and 2 mW output power.In some embodiments, the OCT source 10 is a SLD centered at 830 nm witha spectral bandwidth of about 60 nm that achieves approximately 4 μmdepth resolution in the eye.

In some embodiments, optical element 22 is a scanning mirror. In certainembodiments, optical element 22 is a dichroic beam splitter. Opticalelement 22 can scan and de-scan OCT light and LSLO light on or along theeye 34. In the OCT mode, optical element 22 scans one dimension of theraster scan. In the LSLO mode, optical element 22 scans a line of lightalong the eye 34. In some embodiments, optical element 18 is a scanningmirror. In certain embodiments, optical element 18 is a dichroic beamsplitter. Optical element 18 can scan and descan OCT light on or alongthe eye 34. In the OCT mode, optical element 18 scans the seconddimension of the retina scan. In the LSLO mode, optical element 18 canbe stationary. Optical element 18 reflects LSLO light to optical element26.

Optical element 18 can be a beam separator with an aperture. A dichroicbeam splitter can be disposed in the aperture. In the LSLO mode, thedichroic beam splitter in the aperture passes the beam of light from theLSLO source through a second surface of the dichroic beam splitter tothe retina of the eye. When operating in the LSLO mode, optical element18 can also be a beam separator that separates light directed to the eyefrom light returning from the eye and can redirect the light returningfrom the eye to the detection system. In the OCT mode, the dichroic beamsplitter, which can be disposed in the aperture of optical element 18can scan, using the first surface, the beam of light along the retina ofthe eye in the first dimension and descan, using the first surface, thelight returning from the eye in the first dimension to the detectionsystem. In a preferred embodiment, optical element 18 is used forscanning in the OCT mode, but is not used for scanning in the LSLO mode.

In some embodiments, optical element 26 is a dichroic beam splitter thatreflects OCT light in the OCT mode. Optical element 26 can also be adichroic beam splitter that passes LSLO light in the LSLO mode.

In some embodiments, the grating 46 is a transmission grating. Thegrating 46 can be a holographic diffraction grating (e.g., a gratingavailable from Wasatch Photonics with 1200 lines per mm). The detectiondevice 54 can be a linear array detector. For example, the detectiondevice can be a CCD array or a CMOS detector.

The imaging apparatus 6 can run in three modes: LSLO mode only, OCT modeonly, and frame-interleaved LSLO/OCT mode. The detection device 54 canrecord a sequence of OCT images and LSLO images. In some embodiments, nomoving parts are required to change imaging modes: a simple softwareswitch controls the hardware configuration for each imaging mode “on thefly”. When switched, the desired source can be turned on (and the otheroff) and the camera gain is changed if necessary, as are the transversescan parameters of the data acquisition card. Thus, the LSLO and OCTsystems can be integrated in a unique manner with a common detectionpath that conserves sub-system capabilities and minimizes size, cost,and complexity.

In some embodiments, an OCT image is recorded first. In otherembodiments, a LSLO image is recorded first. In some embodiments, thedetection device in the OCT mode receives light returning from the eyein the first dimension and provides a first electrical responsive to thefirst light at a plurality of locations along a one dimensionaldetector. The electrical signal can be combined with a reference signalfrom a reference arm where the first electrical signal and the referencesignal is associated with an OCT image of the eye. In some embodiments,the detection device in the LSLO mode receives light returning from theeye and provides a second electrical signal responsive to the secondlight at a plurality of locations along the one-dimensional detector.The second electrical signal can be indicative of an LSLO image of theeye.

The CCD array can be a line scan camera (e.g., Atmel AVIIVA M2 CL 1014or an array available from Basler Vision Technologies). The CCD arraycan have 1024 detector pixels with a 14 μm pitch and can operate at amaximum 60 MHz data rate. The output of the camera can be connected to acamera link board (NI PCI-1429). The sampled data can be transferredcontinuously to computer memory. A λ to ω (or k) interpolation can beperformed. A discrete Fourier transform can be performed on each set of1024 data points acquired by the CCD array to produce an axial depthprofile of the sample (A-line).

The CMOS detector can be a linear array detector. In one embodiment, thedetector is a 512 pixel (21 μm pitch) linear CMOS detector with activereset technology with high sensitivity and low read noise (e.g.,available from Fairchild Imaging). In one embodiment, the detector is a2048 pixel (7 μm pitch) CMOS detector with line rates to 40 kHz.

In some embodiments, a controller is associated with the detectionsystem that switches the imaging apparatus between the OCT mode and theLSLO mode. In some embodiments, imaging modes can be switched fastenough to interleave LSLO and SDOCT images. The images can beinterleaved at any desired rate and in any desired sequence orcombination, using software control with no mechanical mode-switchingtransients. The device can rapidly toggle back and forth between LSLOmode and SDOCT mode frame by frame, coordinated by the scanning andsignal processing electronics, e.g., to give the appearance that bothoperate at once: SDOCT on the forward scan, and LSLO on the flyback ofthe scan.

Components of the imaging apparatus 6 can be contained within a housing60. In some embodiments, the housing 60 can be compact and hand-held.The OCT system can be a SDOCT.

FIG. 2 demonstrates another embodiment of a hybrid imaging apparatus 61for imaging the eye 34. First optical element 18′ can be a mirror 20with a dichroic beam splitter 19 mounted in an aperture of the mirror20. The dichroic beam splitter 19 can be mounted on an x-axisgalvanometer. When the light returns from the eye, the first surface ofthe optical element 18′ can be used to redirect the light to thedetection system 54.

In the OCT mode, the first surface of the optical element 18′ scans thelight traveling to the eye 34 in a raster scan and redirects the lightreturning from the eye 34. The optical element 18′ can descan the light.In the LSLO mode, light from source 14 travels through the secondsurface of optical element 18′ to the retina of the eye. The light cantravel to optical element 22 which can be driven by a galvanometer 23that drives the optical element 22 in a direction along the y-axis. Thescanning lenses 38 can include a objective lenses 24 and anophthalmoscopic lens 25.

The imaging lens 50 can be a system of imaging lenses. For example, aplurality of objectives 51A-D can gather light returning from the eye inthe OCT mode or the LSLO mode and direct the light to the detectionsystem 54.

A collimating lens 66 can be used to adjust the optical elements tomaximize the quality of the image. In the LSLO mode, light from the LSLOsource 14 can be directed through a waveguide 67 to a coupler 68, andfrom the coupler 68 to a first collimating lens 66, which directs thelight to the cylindrical lens 58.

In some embodiments, an SDOCT system includes light source 10 and afiber-optic interferometer 69. The fiber optic interferometer 69 caninclude a coupler 79 that receives and/or directs light to four arms:the illumination arm, the sample arm, the reference arm, and thedetection arm. In some embodiments, the coupler is a 50/50 or a 80/20fiber optic beam-splitter. Light from the light source 10 can bedirected to the coupler 79 via waveguide 70. The coupler 79 can dividethe light and direct a portion to the sample arm via waveguide 74 and aportion to the reference arm via waveguide 78. A fraction of the lighttransmitted to the sample arm can be backscattered from the sample, andpassed back into the coupler 79. A fraction of the light transmitted tothe reference arm can be backscattered from an optical delay line (ODL)80, passed back into the coupler 79.

The optical delay line 80 can include a mirror placed on a translationstage and a neutral density filter that adjusts this arm's power level.The optical delay line 80 can be placed in the reference arm to adjustthe length of this arm to match the length of the sample arm. Thepolarization of the reference beam can be adjusted with a paddlepolarization controller to match the polarization of the light from thesample arm, so that polarization changes caused by bending and rotationof the optical fiber in both the sample and reference arms do not washout the interference fringes. The coupler 79 can mix the reference beamwith the light returning from the sample arm. In some embodiments, thislight passes back to the input arms, being equally split between thedetector arm and the illumination arm. The light is sent to the detectorarm through a waveguide 43. An isolator can be placed in theillumination arm to prevent this light from going back to the lightsource 10. Light from waveguide 74 can be directed to a secondcollimating lens 66 via a coupler 81.

The SDOCT system also includes a spectrometer system. The light directedto the detector arm from waveguide 43 passes through coupler 82 and to athird collimating lens 66. The light is dispersed by a grating 46 andreceived by the detection device 54.

FIG. 3 shows a schematic of the command lines, imaging raster, andtiming sequence according to an illustrative embodiment of the imagingapparatus. In some embodiments, an image acquisition board (IMAQ) 86e.g., a cameralink framegrabber is used for data collection while a dataacquisition (DAQ) board 90 is used for instrument timing. The analogoutput 91 can be used to control galvometer(s) 92 that control opticalelement 22. A first digital line 93 can be to turn “on” and “off” any ofthe light sources for the OCT light source 10 or the LSLO light source14. A second digital line, the real time system integration line (RTSI)94 can be used to control the camera gain. The IMAQ 86 provides controlsignals 96 and receives data 97 from the detection device 54. Thecontrol signal 96 can be a gain control for the detection device 54.

In certain embodiments, the detection device 54 is operated in a highgain mode when the imaging apparatus is operating in LSLO mode and a lowgain mode when the imaging apparatus is operating in OCT mode. The OCTis an interferometric measurement, which functions with the least noisewhen the amplifying reference beam power is set to the maximum valuethat will not saturate the camera at its lowest gain (sensitivity)setting. This can give the maximum possible fringe amplitude (OCTsignal) relative to camera noise and digitization levels. The LSLO is adirect imaging method that can rely on high camera sensitivity to imagethe weak fundus reflectance. In some embodiments, the camera gainsetting for the LSLO is the maximum value available that does notsaturate, in order to maintain the best digital resolution over thedynamic range. In some embodiments, the optimal camera gains for the OCTand the LSLO are different and require the gain to be toggledelectronically between two values in switching between imaging modes sothat the performance is optimized for each mode. Alternatively, the LSLOinput beam power can be set higher to account for the requiredsensitivity difference (e.g., up to a limit set by ANSI eye safetystandards). The gain of cameras (e.g., the ATMEL line scan camera) canbe changed with serial digital commands, or more directly with digitalcontrol signals synchronized to the frame rates.

The timing diagram 98 shows the combined LSLO/OCT mode when OCT data canbe acquired. A comparison of the OCT source modulation 102 and the LSLOsource modulation 106 shows that the OCT light source is turned “on”while the LSLO source is turned “off”. In some embodiments, theamplitude of the y-galvanometer 110 versus the amplitude of thex-galvanometer 114 over time is such that the y-galvanometer moves tothe selected y-coordinate, and the x-galvanometer scans the OCT beamover a smaller distance. In diagram 118, the distance covered by theLSLO raster scan 122 is compared to the distance covered by the OCT scan126.

FIG. 4 demonstrates another embodiment of the imaging apparatus 128using moveable parts to operate the apparatus in the LSLO and OCT modes.FIG. 4 shows the LSLO and OCT beams paths separated for clarity. Themoveable parts can include a removable cylindrical lens 58 and a flipmirror 134. The lens moves between a first lens position 58 and a secondlens position 58′ to convert between the LSLO mode and the OCT mode. Themirror can move between a first mirror position 134 and a second mirrorposition 134′ to convert between the LSLO mode and the OCT mode.

A single source 13 can be used to supply light in both the LSLO and OCTmode. In some embodiments, optical element 130 allows both the OCT andLSLO beam to travel through an aperture 131. In the OCT mode, the optic130 can permit the returning light to pass through the same path (e.g.,through the aperture 131), but in the LSLO mode, directs the beam to thedetection system 54. For example, a surface above, below, or surroundingthe aperture can 131 can reflect the light in the LSLO mode. The opticalelement 130 can be a mirror. The same detection system 54 can also beused for both the LSLO and OCT modes.

In the LSLO mode, in the first lens position, the lens 58 receives abeam of light from the source 13 and provides a line of light forscanning an object. The beam travels through optical element 130 tooptical element 22, which scans, through a scanning lens(es) 38 the eye34. The light returning from the eye can be descanned by optical element22 and directed to the detection device 54 by the optical element 130.In the LSLO mode, the flip mirror 134 is flipped out.

In the OCT mode, in the second lens position, the lens 58′ is removedfrom the path of the beam of light so that the source 13 provides thebeam of light for scanning the object. The beam of light can travelthrough optical element 130 to optical element 22, which scans the lightin a raster pattern over a portion of the eye 34. The light returningfrom the eye is directed by optical element 22 to optical element 130.The light can pass back through the pupil, which functions as aninterferometer. The light travels through the sample arm to the coupler79, which mixes the beam with the light from a reference arm as shown inFIGS. 2-3. A part of the mixed beam from the coupler 79 is sent to thedetector arm where the beam is dispersed by the grating 46. In the OCTmode, the flip mirror 134′ directs the light dispersed by the grating 46to the detection device 54.

Without the cylindrical lens 58′ in the beam path and the mirror 134′flipped in, the system can operate as a high-resolution 30 fps SDOCTscanner showing cross-sectional image of the retina at selected planes.With the lens 58 in place and the mirror 134 flipped out, the SLD beamcan be fanned into a focused line, and the system can be converted intoa quasi-confocal LSLO en face wide-field retinal imager. In someembodiments, the actuated cylindrical lens 58 and mirror 134 permit modeswitching within less than about 1 frame period. The SLD source modulecan be integrated into the optics package. A tether can be used connectto an external source and power module. In certain embodiments,batteries can be used.

FIG. 5 shows another illustrative embodiment of an imaging apparatus 138that includes moveable parts to convert between an OCT mode and an LSLOmode. The same light source 13 and detection system 54 can be used forboth the OCT mode and LSLO mode. Light source 13 directs light tocoupler 140 via waveguide 142 in the sample arm.

In the LSLO mode, the coupler 140 directs light to the lens 58, whichdirects light to optical element 144. Optical element 144 directs lightto optical element 22, which can scan the beam of radiation on the eye34, Light returning from the eye 34 passes by and/or around opticalelement 144 and through pupil stop 146. Flip mirror 134 is removed fromthe optical path.

In the OCT mode, lens 58 is in position 58′ (e.g., it is removed fromthe beam path). The light is directed by optical element 144 to opticalelement 22. Light returning from the eye 34 is reflected by opticalelement 144 back into waveguide 142. The light emerges from waveguide 43and is dispersed by grating 46 before it is reflected by mirror 134 tothe detection device 54.

Optical element 144 can be a mirror or prism. Optical element 146 can bea pupil stop and/or a pupil aperture. The subdivision of the pupilaperture can allow the efficient integration of the subsystems andelimination of unwanted reflections (e.g., corneal reflections). In someembodiments, the scanning optical delay in the OCT reference arm 78compensates for pupil position, eye length and/or focus. With a flipmirror 134, both imaging systems can use the same linear array detector54.

The linear image sensor, the spectrometer, the image acquisition, andthe processing electronics can reduce the cost and complexity of ahybrid imaging system. FIG. 6 shows a block diagram of an exemplarychipset 160. A stand-alone FPGA/DSP electronics platform (e.g., nottethered to a PC) can be used for real-time LSLO and OCT signalprocessing and integrated display. The chipset 160 can include a cameralink 164, a signal processor 168, a video encoder 172, memory 176, astorage module 180, a USB controller 184, and a user interface 188.

The camera link 164 can be coupled to the detection device 54. The videoencoder can be coupled to a display device 192. The memory 176 can beSDRAM, flash memory, and/or any other suitable memory. The storagedevice 180 can be a compact flash, smart media, SD, or MMC. The USBcontroller can include a USB interface.

The user interface 188 and display device 192 can display an LSLO imageand a OCT image separately or simultaneously (depending on the imagingmode), and the OCT scan can be positioned anywhere in the LSLO raster.Other controls for OCT processing, display, and saving or streaming todisk are in a tab box in the display. The raw spectrum and processedprofile can be shown, and the integrated fixation target can bedisplayed.

In some embodiments, an FPGA camera board with integrated SVGA LCDdisplay driver for a CMOS line array can obviate the need for a PC andframe grabber tethered to the optical scanner head. In certainembodiments, real time FFTs on SDOCT line scan data and display can beperformed using the signal processor chipset 168 (e.g., a DM642fixed-point DSP or an FPGA). The detection device 54 can be connected tothe signal processor via camera-link RX Chipset 164. A suitable signalprocessing approach or algorithm with associated hardware and softwarefor SDOCT signal processing algorithm can include such an interpolationto k-space process. Dispersion compensation can be incorporated in thesoftware for real time operation.

LSLO-guided 2D SDOCT sections and localized 3D (micro-scan) SDOCTimaging modalities can be used as part of the imaging mode controlsoftware. In some embodiments, by overlaying a fiducial line or box overthe live LSLO image display, which represents the length, position andorientation of the SDOCT scan(s) to be captured in the next frame(s),the operator can precisely scan selected retinal features at the desiredresolution. 3D structure can be visualized by sweeping the line scanmanually push broom-style.

In some embodiments, local 3D images can be captured and displayed(e.g., a micro-scan option). In some embodiments, a resonant scanner isused to perform a low speed, small amplitude scan. The resonant scannercan be added to the SDOCT beam path, orthogonal to the main galvoscanner. Instead of performing a single long linear scan of 5 mm or morewhen a very small feature such as a laser lesion is of interest, thesystem can be commanded to perform many smaller scans in a rasterpattern: perhaps twenty or more 0.5 mm B-scans with 10 micronpixellation in x (50 A-scans) and 25 μm pixels in y (20 B-scans). Thus,the entire raster can include 1000 A-scans, which can be displayed asone composite B-scan. 500×500 micron×2 mm high-resolution SDOCT volumeimages can be provided. Such an approach can be used for elucidatingcolumnar laser damage or localized pathology. A fiducial box can beoverlaid in the live LSLO image for this selectable mode, with real timedisplay of the successive SDOCT stripe images.

Estimates of 3D micro-scan speed can be obtained from digital signalprocessor benchmark data. The 1024 point FFT benchmark for the DM642 isless than about 16 μs per FFT. The CCD array or CMOS detector can haveline rates in excess of 25 Klps. At this line rate, the resulting framerate for 1000 A-scans of the Micro-scan raster (50×20) is about 25 fps(0.04 sec/frame). Real time 3D micro-scans with rapid intuitive displayof 3D data can be performed. In some embodiments, a FPGA signalprocessor is utilized to provide a scan showing local 3D structures.

While the invention has been particularly shown and described withreference to specific illustrative embodiments, it should be understoodthat various changes in form and detail may be made without departingfrom the spirit and scope of the invention.

What is claimed:
 1. A method of imaging a retina of an eye, comprising:combining an optical path of an optical coherence tomography (OCT)imager and an optical path of a line scanning laser ophthalmoscope(LSLO) imager using a system of optics; using a single detector toswitch between an OCT mode and a LSLO mode; and acquiring images of theretina while switching between the OCT mode and the LSLO mode.
 2. Themethod of claim 1 further comprising interleaving a first series ofimages of the retina acquired in the OCT mode and a second series ofimages of the retina acquired in the LSLO mode.
 3. The method of claim 1wherein the system of optics is disposed in a housing capable ofoperating in the LSLO mode and the OCT mode, the system of opticsincluding: a first source to provide a first beam of light for the OCTimager; a second source to provide a second beam of light for the LSLOimager; and a first optic that: in the OCT mode, (i) scans, using afirst surface of the first optic, the first beam of light along a retinaof an eye in a first dimension, and (ii) descans, using the firstsurface, a first light returning from the eye in the first dimension tothe single detector; and in the LSLO mode, (i) passes, through a secondsurface of the first optic, the second beam of light to the retina ofthe eye.
 4. The method of claim 3 wherein the single detector comprisesa one-dimensional detector that: in the OCT mode, receives the firstlight returning from the eye in the first dimension and provides a firstelectrical signal responsive to the first light at each of a pluralityof locations along the one-dimensional detector, the first electricalsignal combined with a reference signal from a reference arm, the firstelectrical signal and the reference signal associated with an OCT imageof the eye; and in the LSLO mode, receives a second light returning fromthe eye and provides a second electrical signal responsive to the secondlight at each of a plurality of locations along the one-dimensionaldetector, the second electrical signal indicative of a LSLO image of theeye.
 5. The method of claim 4 wherein the system of optics furthercomprises: a second optic that: in the OCT mode, (i) scans the firstbeam of light along the retina in a second dimension, and (ii) descansthe first light returning from the eye in the second dimension, thefirst light returning from the eye directed to the first surface of thefirst optic and to the single detector; and in the LSLO mode, (i) scansthe second beam of light, in a line focus configuration, along theretina in the second dimension, and (ii) descans the second lightreturning from the eye in the second dimension, the light returning fromthe eye directed to the first surface of the first optic and to thesingle detector.
 6. The method of claim 4 wherein the system of opticsfurther comprises: a third optic that: in the OCT mode, (i) directs,using a first surface of the third optic, the first beam of light to thefirst optic, (ii) redirects, using the first surface of the first optic,the first light returning from the eye scanned, and (iii) redirects,using a second surface of the third optic, the first light, dispersed bya grating, to the single detector; and in the LSLO mode, passes thesecond light returning from the eye to the single detector.
 7. Themethod of claim 3 wherein the first optic comprises: a beam separator,having an aperture, that, in the LSLO mode, redirects the second lightreturning from the eye to the single detector; and a dichroic beamsplitter, disposed in the aperture, that: in the OCT mode, (i) scans,using the first surface of the dichroic beam splitter, the first beam oflight along the retina of the eye in the first dimension, and (ii)descans, using the first surface, the first light returning from the eyein the first dimension to the single detector; and in the LSLO mode, (i)passes, through the second surface of the dichroic beam splitter, thesecond beam of light to the retina of the eye.
 8. The method of claim 5wherein the second optic comprises a scanning mirror.
 9. The method ofclaim 6 wherein the third optic comprises dichroic beam splitter. 10.The method of claim 3 wherein the first source and the second source arethe same source of light.
 11. The method of claim 1 wherein the systemof optics includes a controller, associated with the single detector,that switches the apparatus between the OCT mode and the LSLO mode tointerleave acquisition of an OCT image of the eye and an LSLO image ofthe eye by the single detector.
 12. The method of claim 1 wherein theOCT imager comprises a spectral domain OCT imager.
 13. The method ofclaim 1 wherein the system of optics is disposed in a housing capable ofoperating in the LSLO mode and the OCT mode, the system of opticsincluding: a first optic that: in the OCT mode, (i) redirects, using afirst surface of the optic, a beam of light from a first source to anobject to be scanned, (ii) redirects, using the first surface, lightreturning from the object scanned, and (iii) redirects, using a secondsurface of the optic, light dispersed by a grating to the singledetector; and in the LSLO mode, passes light returning from the objectscanned to the single detector.
 14. The method of claim 13 wherein thesingle detector comprises a one-dimensional detector that: in the LSLOmode, receives light descanned from the object and provides anelectrical signal responsive to the light descanned at each of aplurality of locations along a LSLO line configuration, the electricalsignal indicative of a LSLO image of the object; and in the OCT mode,receives light redirected by the mirror and provides an electricalsignal responsive to the light redirected at each of a plurality oflocations along an OCT line configuration, the electrical signalcombined with a reference signal from a reference arm, the electricalsignal and the reference signal associated with an OCT image of theobject.
 15. The method of claim 13 wherein the first optic comprisesdichroic beam splitter.
 16. The method of claim 1 wherein the system ofoptics is disposed in a housing capable of operating in the LSLO modeand the OCT mode, the system of optics including: a first source of abeam of light suitable for use in the LSLO imager; a second source of abeam of light suitable for use in the OCT imager; a lens receiving thebeam of light from the first source and providing a line of light foruse in the LSLO imager; an optic that: in the OCT mode, (i) redirects,using a first surface of the optic, a beam of light from the secondsource to an object to be scanned, (ii) redirects, using the firstsurface, light returning from the object scanned, and (iii) redirects,using a second surface of the optic, light dispersed into an OCT lineconfiguration by a grating to the single detector; and in the LSLO mode,passes light returning from the object scanned to the single detector;and a scanner that: in the LSLO mode, scans, through at least one lens,a first portion of an object with the line of light in a directionperpendicular to the line, and descans light returning from the objectin a LSLO line configuration; and in the OCT mode, scans a secondportion of the object with the beam of light, and redirects lightreturning from the object; wherein the single detector comprises aone-dimensional detector that: in the LSLO mode, receives the lightdescanned from the object and provides an electrical signal responsiveto the light descanned at each of a plurality of locations along theLSLO line configuration, the electrical signal indicative of a LSLOimage of the object; and in the OCT mode, receives the light redirectedfrom the mirror and provides an electrical signal responsive to thelight redirected at each of a plurality of locations along the OCT lineconfiguration, the electrical signal combined with a reference signalfrom a reference arm, the electrical signal and the reference signalassociated with an OCT image of the object.
 17. The method of claim 16wherein the optic comprises a dichroic beam splitter.
 18. The method ofclaim 16 wherein the OCT imager comprises a spectral domain OCT imager.19. The method of claim 1 wherein the system of optics is disposed in ahousing capable of operating in the LSLO mode and the OCT mode, thesystem of optics including: a lens for converting between the LSLO modeand the OCT mode, the lens movable between a first lens position and asecond lens position: in the first lens position, the lens receives abeam of light from a source and provides a line of light for scanning anobject in the LSLO mode; and in the second lens position, the lensremoved from a path of the beam of light so that the source provides thebeam of light for scanning the object in the OCT mode; and a mirror forconverting between the LSLO mode and the OCT mode, the mirror movablebetween a first mirror position and a second mirror position: in thefirst position, the mirror is removed from a path of light returningfrom the object; and in the second position, the mirror receives thelight returning from the object.
 20. The method of claim 19 wherein thesystem of optics further comprises a scanner that: in the LSLO mode,scans, through at least one lens, a first portion of the object with theline of light in a direction perpendicular to the line, and descanslight returning from the object in the LSLO line configuration; and inthe OCT mode, scans a second portion of the object with the beam oflight, and redirects light returning from the object.
 21. The method ofclaim 20 wherein the single detector is a one-dimensional detector that:in the LSLO mode, receives light descanned from the object and providesan electrical signal responsive to the light descanned at each of aplurality of locations along a LSLO line configuration, the electricalsignal indicative of a LSLO image of the object; and in the OCT mode,receives light redirected by the mirror and provides an electricalsignal responsive to the light redirected at each of a plurality oflocations along an OCT line configuration, the electrical signalcombined with a reference signal from a reference arm, the electricalsignal and the reference signal associated with an OCT image of theobject.
 22. The method of claim 19 wherein the system of optics furthercomprises a source of the beam of light used in the LSLO mode and theOCT mode.
 23. The method of claim 19 wherein the system of opticsfurther comprises a grating spectrograph, used only in the OCT mode,dispersing light returning from the object into an OCT lineconfiguration.
 24. The method of claim 19 wherein the OCT imagercomprises a spectral domain OCT imager.
 25. A method of imaging a retinaof an eye, comprising: acquiring an OCT image of the eye by receiving,on a one-dimensional detector, a first light returning from the eye andproviding a first electrical signal responsive to the first light ateach of a plurality of locations along the one-dimensional detector, thefirst electrical signal combined with a reference signal from areference arm, the first electrical signal and the reference signalassociated with the OCT image of the eye; acquiring a LSLO image of theeye by receiving, on the one-dimensional detector, a second lightreturning from the eye and providing a second electrical signalresponsive to the second light at each of a plurality of locations alongthe one-dimensional detector, the second electrical signal indicative ofthe LSLO image of the eye; and interleaving acquisition of the OCT imageof the eye and the LSLO image of the eye.